作者单位:Univ Wisconsin, Coll Engn & Appl Sci, 3200 North Cramer St, Milwaukee, WI 53211 USA[1]Massachusetts Gen Hosp, Dept Radiol, 55 Fruit St, Boston, MA 02114 USA[2]Mayo Clin, Dept Radiol, 200 First St SW, Rochester, MN 55905 USA[3]Arizona State Univ, Dept Phys, 550 East Tyler Dr, Tempe, AZ 85287 USA[4]